Pad structure design in fan-out package

ABSTRACT

A package includes a corner, a device die, a plurality of redistribution lines underlying the device die, and a plurality of non-solder electrical connectors underlying and electrically coupled to the plurality of redistribution lines. The plurality of non-solder electrical connectors includes a corner electrical connector. The corner electrical connector is elongated. An electrical connector is farther away from the corner than the corner electrical connector, wherein the electrical connector is non-elongated.

BACKGROUND

In the packaging of integrated circuits, there are various types ofpackaging methods and structures. For example, in a conventionalPackage-on-Package (POP) process, a top package is bonded to a bottompackage. The top package and the bottom package may also have devicedies packaged therein. By adopting the PoP process, the integrationlevel of the packages is increased.

In an existing PoP process, the bottom package is formed first, whichincludes a device die bonded to a package substrate. A molding compoundis then molded on the package substrate, wherein the device die ismolded in the molding compound. The package substrate further includessolder balls formed thereon, wherein the solder balls and the device dieare on a same side of the package substrate. The solder balls are usedfor connecting the top package to the bottom package.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of a package in accordancewith some embodiments;

FIG. 2 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, whereincorner electrical connectors are elongated connectors;

FIG. 3 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, wherein aplurality of elongated electrical connectors is distributed to eachcorner;

FIG. 4 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, whereinelongated electrical connectors and non-elongated electrical connectorsare distributed depending on their distances to a neutral-stress pointof the package;

FIG. 5 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, whereininner electrical connectors adjacent to the corners of an overlyingdevice die are elongated;

FIG. 6 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, whereininner electrical connectors adjacent to the corners of an overlyingdevice die group are elongated;

FIG. 7 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, wherein aplurality of inner electrical connectors adjacent to each corner of anoverlying device die is elongated;

FIG. 8 illustrates a bottom view of a package and non-solder electricalconnectors of the package in accordance with some embodiments, wherein aplurality of inner electrical connectors adjacent to each corner of anoverlying device die group is elongated;

FIGS. 9A and 9B illustrate bottom views of some exemplary elongatedelectrical connectors; and

FIGS. 10A and 10B illustrate bottom views of some exemplarynon-elongated electrical connectors.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “under,” “lower,”“over,” “upper” and the like, may be used herein for ease of descriptionto describe one element or feature's relationship to another element(s)or feature(s) as illustrated in the figures. The spatially relativeterms are intended to encompass different orientations of the device inuse or operation in addition to the orientation depicted in the figures.The apparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

A fan-out package is provided in accordance with various exemplaryembodiments. The variations of the embodiments are discussed. Throughoutthe various views and illustrative embodiments, like reference numbersare used to designate like elements.

FIG. 1 illustrates a cross-sectional view of package 20 in accordancewith some embodiments. Package 20 includes bottom package 100, and toppackage 200 over and bonded to bottom package 100. In some embodiments,bottom package 100 includes device dies 102 (including 102A and 102B),with the front sides of device dies 102 facing down and bonded toRedistribution Lines (RDLs) 112. In alternative embodiments, bottompackage 100 includes a single device die or more than two device dies.Device dies 102 may include semiconductor substrates 108, and integratedcircuit devices (such as active devices, which include transistors, forexample) 104 at the front surface (the surface facing down) ofsemiconductor substrate 108. Device dies 102 may include logic dies suchas Central Processing Unit (CPU) dies, Graphic Processing Unit (GPU)dies, mobile application dies, or the like.

Device dies 102 are molded in molding material 120, which surroundsdevice dies 102. Molding material 120 may be a molding compound, amolding underfill, a resin, or the like. The bottom surface 120A ofmolding material 120 may be leveled with the bottom ends of device dies102. The top surface 120B of molding material 120 may be level with orhigher than back surface 108A of semiconductor substrate 108. In someembodiments, back surfaces 108A of semiconductor substrates 108 areoverlapped by dielectric films 110, which adhere device dies 102 to theoverlying dielectric layer 118 and RDLs 116. Device dies 102 furtherincludes metal pillars 106 (which may include copper pillars) in contactwith, and bonded to, RDLs 112.

Bottom package 100 may include bottom-side RDLs 112 underlying devicedies 102, and top-side RDLs 116 overlying device dies 102. Bottom-sideRDLs 112 are formed in dielectric layers 114, and top-side RDLs 116 areformed in dielectric layers 118. RDLs 112 and 116 may be formed ofcopper, aluminum, nickel, alloys thereof, or multi-layers thereof. Insome embodiments, dielectric layers 114 and 118 are formed of inorganicmaterial such as silicon oxide, silicon nitride, silicon oxynitride, orthe like. In alternative embodiments, dielectric layers 114 and 118 areformed of organic materials such as polymers, which may further includepolybenzoxazole (PBO), benzocyclobutene (BCB), polyimide, or the like.

Through-Vias 122 are formed to penetrate through molding material 120.In some embodiments, through-vias 122 have top surfaces level with thetop surface of molding material 120, and bottom surfaces level with thebottom surface of molding material 120. Through-Vias 122 electricallyconnect bottom-side RDLs 112 to top-side RDLs 116. Through-Vias 122 mayalso be in physical contact with bottom-side RDLs 112 and top-side RDLs116.

Electrical connectors 124, which are formed of a non-solder metallicmaterial(s), are formed at the bottom surface of bottom package 100. Insome embodiments, electrical connectors 124 are metal pads. Inalternative embodiments, electrical connectors 124 include metal pillarssuch as copper pillars. Throughout the description, electricalconnectors 124 are referred to as metal pads 124, although they may haveother forms. In accordance with some embodiments, metal pads 124comprise copper, aluminum, nickel, palladium, gold, or multi-layersthereof. In some embodiments, as shown in FIG. 1, the bottom surfaces ofmetal pads 124 are level with the bottom surface of the bottomdielectric layer 114. In alternative embodiments, the bottom surfaces ofmetal pads 124 extend below the bottom surface of the bottom dielectriclayer 114. Solder regions 126 are attached to the bottom surfaces ofmetal pads 124, and bond bottom package 100 to package component 300. Insome embodiments, package component 300 comprises a Printed CircuitBoard (PCB).

In some embodiments, top package 200 includes package substrate 202, anddevice die 204 bonded to package substrate 202. The bonding of devicedie 204 to package substrate 202 may be achieved through wire bonding,flip-chip bonding, or the like. Solder regions 206 bond top package 200to bottom package 100, wherein solder regions 206 may be in contact withtop-side RDLs 116.

FIG. 2 illustrates a bottom view of bottom package 100, wherein metalpads 124 are illustrated. Metal pads 124 include elongated metal pads124A and non-elongated metal pads 124B. In FIGS. 2 through 8, circlesare used to schematically represent non-elongated metal pads 124B, andovals are used to schematically represent elongated metal pads 124A.FIGS. 9A and 9B illustrate a bottom view (or a top view) of someexemplary elongated metal pad 124A. Elongated metal pad 124A has lengthL1 measured in lengthwise direction X, and width W1 measured inwidthwise direction Y, which is perpendicular to lengthwise direction X.Length L1 is greater than width W1. Elongated metal pad 124A includeslonger axis 134 in lengthwise direction X, and shorter axis 136 inwidthwise direction Y. Throughout the description, an elongated metalpad 124A is a metal pad whose length-to-width ratio L1/W1 is greaterthan a threshold ratio Lt that is greater than 1. Threshold ratio Lt maybe greater than about 1.2, greater than about 1.6, or greater than about2.0.

Elongated metal pad 124A may have various shapes including, and notlimited to, an oval shape, a rectangular shape, an elongated octagonshape, or the like. For example, FIG. 9A illustrates an exemplaryelongated metal pad 124A, which includes two half circles 130 connectedto opposite edges of rectangle 128. FIG. 9B illustrates an elongatedhexagon.

FIGS. 10A and 10B illustrate the bottom views (or top views) ofexemplary non-elongated metal pads 124B. Throughout the description, anon-elongated metal pad 124B does not have length L2 and width W2observably different from each other. Alternatively, a non-elongatedmetal pad 124B has width W2 smaller than length L2, with length-to-widthratio L2/W2 being smaller than the threshold ratio Lt. For example,FIGS. 10A and 10B illustrate non-elongated metal pads 124B, which have acircular bottom-view shape and a hexagon bottom-view shape,respectively.

Although not shown in FIGS. 9A, 9B, 10A, and 10B, the bottom views ofsolder regions 126 (FIG. 1) are defined by, and may be the same as, thebottom-view shapes of the respective overlying metal pads 124. Hence,solder regions 126 may also include elongated solder regions andnon-elongated solder regions.

Referring back to FIG. 2, bottom package 100 includes four corners 138.The corner metal pads 124, which are closer to the respective corners138 than all other metal pads, are elongated metal pads 124A. Othermetal pads 124 that are farther away from the respective corners 138than the corner metal pads 124A are non-elongated metal pads 124B. Insome embodiments, there may be more than one elongated metal pad 124A ateach corner 138. For example, as shown in FIG. 3, there are threeelongated metal pads 124A at each corner 138.

FIGS. 3 and 4 illustrate the bottom view of bottom package 100 and metalpads 124 in accordance with alternative embodiments. In the bottom view,bottom package 100 has neutral-stress point 140, which is the point thatis substantially free from stresses from all lateral directions that areparallel to the bottom surface of package 100. At neutral-stress point140, the lateral stresses from opposite directions are cancelled out. Insome embodiments, neutral-stress point 140 is at or close to the centerof bottom package 100 (in the bottom view). The distance of each ofmetal pads 124 to neutral-stress point 140 is referred to as a Distanceto Neutral Point (DNP) of the respective metal pad, wherein the distanceof the metal pad is measured from a point of the metal pad that isclosest to neutral-stress point 140. For example, DNPs DNP1 and DNP2 areillustrated as examples in FIG. 3.

A circle 142 is drawn with the neutral-stress point 140 as the center,wherein circle 142 has radius r. In accordance with the embodiments ofthe present disclosure, all metal pads 124 with DNPs equal to or smallerthan radius r are designed as non-elongated metal pads 124B, and allmetal pads 124 with DNPs greater than radius r are designed to beelongated metal pads 124A. As illustrated in FIG. 3, if radius r islarge, then the elongated metal pads include corner metal pads. In theseembodiments, each row includes at least one (or more) metal pad that isthe non-elongated metal pad. In FIG. 4, radius r is reduced, and hencean entire edge-row or edge-column of metal pads 124 whose DNPs aregreater than radius r are elongated, while the metal pads 124 with theDNPs equal to or smaller than radius r are non-elongated. In theembodiments in FIGS. 3 and 4, the elongated metal pads 124A includecorner pads.

FIG. 5 illustrates the bottom view of bottom package 100 and metal pads124 in accordance with yet alternative embodiments. Device die 102 isillustrated in the bottom view. Device die 102 includes corners 146. Insome embodiments, the inner metal pads 124 (which are not edge pads andnot corner pad) that are overlapped by device die 102, which inner pads124 are also closest to corners 146, are elongated metal pads 124A,while other metal pads 124 (except the metal pads 124A discussed in theembodiments in FIGS. 2 through 4) are non-elongated metal pads 124B. Insome embodiments, the inner elongated metal pads 124A are surrounded bynon-elongated metal pads 124B.

FIG. 6 illustrates the bottom view of bottom package 100 and metal pads124 in accordance with yet alternative embodiments. In theseembodiments, a plurality of device dies 102 is closely located from eachother to form device die group 148. Device die group 148 includescorners 146. In some embodiments, the inner metal pads 124 that areoverlapped by device die group 148, which metal pads 124 are alsoclosest to corners 146, are elongated metal pads 124A, while other metalpads 124 (except the metal pads 124A discussed in the embodiments inFIGS. 2 through 4) are non-elongated metal pads 124B. In someembodiments, the inner elongated metal pads 124A are surrounded bynon-elongated metal pads 124B. In these embodiments, some metal pads 124(marked as 124′) that are close to the corners of devices dies 102, butare not close to the corners 146 of device die group 148, may benon-elongated metal pads 124B.

FIGS. 7 and 8 illustrate the bottom views of bottom package 100 andmetal pads 124 in accordance with yet alternative embodiments. Theseembodiments are similar to the embodiments in FIGS. 6 and 7, except thatmore metal pads 124 that are close to the corners of device dies 102 ordevice die group 148 are elongated metal pads 124A, which are surroundedby non-elongated metal pads 124B. FIG. 7 illustrates a single device die102, with elongated metal pads 124A being distributed close to thecorners 146 of device die 102. FIG. 8 illustrates a device die group148, with elongated metal pads 124A being distributed close to thecorners 146 of device die group 148. In accordance with some embodimentsin FIGS. 5 through 8, an inner elongated metal pad 124A may be fully, orpartially, overlapped by the overlying device die 102 or device diegroup 148.

Throughout the embodiments of the present disclosure, as shown in FIGS.2 through 8, elongated metal pads 124A are centripetal. This means thatthe longer axis (FIGS. 9A and 9B) of elongated metal pads 124A extendtoward the neutral-stress point 140, which may be, or at least close to,the center of bottom package 100 (in the bottom view). Alternativelystated, the longer axis 134 (FIGS. 9A and 9B) passes through the centerof bottom package 100, or at least, the longer axis 134 is closer to thecenter of bottom package 100 than the shorter axis 136.

The embodiments of the present disclosure have some advantageousfeatures. Simulation results indicated that when the corner metal padsof the bottom package 100 are centripetal elongated metal pads, therespective package fails after 769 thermal cycles in the reliabilitytest. As a comparison, when the corner metal pads of the bottom package100 are non-elongated metal pads, the respective package fails after 604thermal cycles. When the corner metal pads of the bottom package 100 areelongated metal pads with the widthwise directions extending toward theneutral-stress point, the respective bottom package fails after 574thermal cycles. These results indicate that the package with thecentripetal elongated metal pads have improved reliability.

In accordance with some embodiments of the present disclosure, a packageincludes a corner, a device die, a plurality of redistribution linesunderlying the device die, and a plurality of non-solder electricalconnectors underlying and electrically coupled to the plurality ofredistribution lines. The plurality of non-solder electrical connectorsincludes a corner electrical connector. The corner electrical connectoris elongated. An electrical connector is farther away from the cornerthan the corner electrical connector, wherein the electrical connectoris non-elongated.

In accordance with alternative embodiments of the present disclosure, apackage includes at least one first dielectric layer, a first pluralityof redistribution lines in the at least one first dielectric layer, adevice die over and electrically coupled to the first plurality ofredistribution lines, a molding material molding the device die therein,and a through-via penetrating through the molding material. At least onesecond dielectric layer is over the device die. A second plurality ofredistribution lines is in the at least one second dielectric layer,wherein the second plurality of redistribution lines is electricallycoupled to the first plurality of redistribution lines through thethrough-via. A plurality of metal pads is underlying the device die andelectrically coupled to the second plurality of redistribution lines.The plurality of metal pads includes a first elongated metal pad and anon-elongated metal pad.

In accordance with yet alternative embodiments of the presentdisclosure, a package includes a plurality of dielectric layers, aplurality of redistribution lines in the plurality of dielectric layers,a device die over and electrically coupled to the plurality ofredistribution lines, and a plurality of non-solder electricalconnectors underlying and electrically coupled to the plurality ofredistribution lines. The plurality of non-solder electrical connectorsincludes a corner electrical connector and an inner electricalconnector. The corner electrical connector and the inner electricalconnector are elongated, and are centripetal. A plurality ofnon-elongated electrical connectors surrounds the inner electricalconnector.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A package comprising: a bottom packagecomprising: a corner; a first device die; a plurality of redistributionlines underlying the first device die; a plurality of non-solderelectrical connectors underlying and electrically coupled to theplurality of redistribution lines, wherein the plurality of non-solderelectrical connectors comprises: a corner electrical connector, whereinthe corner electrical connector is elongated; and an electricalconnector farther away from the corner than the corner electricalconnector, wherein the electrical connector is non-elongated; and adielectric layer, with the plurality of non-solder electrical connectorsin the dielectric layer; and a solder region forming an elongatedinterface with the corner electrical connector, wherein the elongatedinterface is coplanar with a bottom surface of the dielectric layer. 2.The package of claim 1, wherein at each of corners of the bottompackage, there is an elongated one of the plurality of non-solderelectrical connectors.
 3. The package of claim 1, wherein the pluralityof non-solder electrical connectors comprises an inner elongatedconnector adjacent to a corner of the first device die, and wherein theplurality of non-solder electrical connectors further comprises aplurality of additional non-elongate connectors surrounding the innerelongated connector, wherein all non-solder electrical connectorsimmediately neighboring the inner elongated connector are elongated. 4.The package of claim 1 further comprising a second device die over andbonded to the plurality of redistribution lines, wherein the firstdevice die and the second device die are in a die group, wherein theplurality of non-solder electrical connectors comprises inner elongatedconnectors adjacent to all corners of the die group, and wherein theinner elongated connectors are surrounded by non-elongated connectorsamong the plurality of non-solder electrical connectors.
 5. The packageof claim 1, wherein the bottom package has a neutral-stress point in abottom view of the bottom package, wherein all connectors in theplurality of non-solder electrical connectors and having Distances toNeutral Point (DNPs) greater than a radius are elongated, and whereinall connectors in the plurality of non-solder electrical connectors andhaving DNPs equal to or smaller than the radius are non-elongated. 6.The package of claim 1, wherein the elongated interface is centripetal.7. The package of claim 1 further comprising a top package over andbonded to the bottom package.
 8. A package comprising: at least onefirst dielectric layer; a first plurality of redistribution lines in theat least one first dielectric layer; a device die over and electricallycoupled to the first plurality of redistribution lines; a moldingmaterial molding the device die therein; a through-via penetratingthrough the molding material; at least one second dielectric layer overthe device die; a second plurality of redistribution lines in the atleast one second dielectric layer, wherein the second plurality ofredistribution lines is electrically coupled to the first plurality ofredistribution lines through the through-via; a plurality of metal padsunderlying the device die and electrically coupled to the secondplurality of redistribution lines, wherein the plurality of metal padscomprises a first elongated metal pad and a non-elongated metal pad, andthe plurality of metal pads is non-solder metal pads; and a bottomdielectric layer in the at least one first dielectric layer, with theplurality of metal pads being in the bottom dielectric layer, wherein abottom surface of the first elongated metal pad is planar and coplanarwith a bottom surface of the bottom dielectric layer, and the bottomsurface of the first elongated metal pad is elongate and centripetal. 9.The package of claim 8, wherein the first elongated metal pad is acorner metal pad.
 10. The package of claim 8, wherein all corner metalpads in the plurality of metal pads are elongated.
 11. The package ofclaim 8, wherein the first elongated metal pad is centripetal, with alengthwise direction of the first elongated metal pad extending toward acenter of the package.
 12. The package of claim 8 further comprising asecond elongated metal pad, wherein the second elongated metal pad isadjacent to a corner of the device die in a bottom view of the package,wherein at least a portion of the second elongated metal pad isoverlapped by a portion of the device die.
 13. The package of claim 12,wherein the second elongated metal pad is fully sounded by non-elongatedmetal pads, wherein all metal pads immediately neighboring the secondelongated metal pad are non-elongated.
 14. The package of claim 8further comprising: a plurality of solder regions adjoined to theplurality of metal pads; and a Printed Circuit Board (PCB) bonded to thepackage through the plurality of solder regions.
 15. A packagecomprising: a plurality of dielectric layers; a plurality ofredistribution lines in the plurality of dielectric layers; a firstdevice die over and electrically coupled to the plurality ofredistribution lines; a plurality of non-solder electrical connectorsunderlying and electrically coupled to the plurality of redistributionlines, wherein the plurality of non-solder electrical connectorscomprises: a corner electrical connector, wherein the corner electricalconnector is elongated; a first inner electrical connector, wherein thefirst inner electrical connector is elongated; and a plurality ofnon-elongated electrical connectors surrounding the first innerelectrical connector, wherein non-solder electrical connectors immediateneighboring the first inner electrical connector are non-elongated. 16.The package of claim 15, wherein the all non-solder electricalconnectors immediately neighboring the first inner electrical connectorcomprises: a first electrical connector and a second electricalconnector, wherein the first electrical connector, the second electricalconnector, and the first inner electrical connector are aligned to afirst straight line; and a third electrical connector and a fourthelectrical connector, wherein the third electrical connector, the fourthelectrical connector, and the first inner electrical connector arealigned to a second straight line perpendicular to the first straightline, and wherein no additional electrical connector separates the firstinner electrical connector from the first, the second, the third, andthe fourth electrical connectors.
 17. The package of claim 15, whereinthe first inner electrical connector comprises a portion overlapped byat least a part of the first device die.
 18. The package of claim 15further comprising a second device die over and electrically coupled tothe plurality of redistribution lines, wherein the first device die andthe second device die are in a die group, and wherein each of corners ofthe die group is adjacent to an elongated connector that is among theplurality of non-solder electrical connectors.
 19. The package of claim15 further comprising: a dielectric layer, with the plurality ofnon-solder electrical connectors being in the dielectric layer; and asolder region forming a planar oval interface with the first innerelectrical connector, wherein the planar oval interface is coplanar withan outer surface of the dielectric layer.
 20. The package of claim 15,wherein length-to-width ratios of the corner electrical connector andthe first inner electrical connector are higher than about 1.2.